The present invention relates to the field of insertion of intra-ocular lenses, and provides an improved device for inserting an intra-ocular lens into the eye.
The original intra-ocular lens (IOL) introduced in 1948 was made of poly(methyl methacrylate), with polypropylene haptics. It was rigid and inflexible and its insertion required a 7 to 9 mm incision in the eye and a stitch to close the wound, with attendant discomfort and the inconvenience of later stitch removal.
With the advent of flexible IOLs made of silicone or acrylate elastomers, which could be folded and inserted into the eye through an incision that might be as small as 2.8 mm or less, no stitch was necessary and the whole procedure was simplified and abbreviated.
The use of flexible IOLs created a need for a device that could guide the lens into the smaller opening in the eye. One example of a device for insertion of an IOL is given in U.S. Pat. No. 4,681,102. Other devices for accomplishing the insertion are described in U.S. Pat. Nos. 5,716,364, 5,803,925, 5,947,976, and 5,976,150. The disclosures of all of the above-cited patents are incorporated by reference herein.
The basic principle embodied in the design of any of the devices shown in the above-cited patents is to provide a lubricious pathway for a folded IOL to be pushed without damage into the corneal chamber (often described as “the bag”) from which the eye's natural lens has been removed, where the IOL can unfold spontaneously.
Clearly, many variations are possible in the mechanical design of the apparatus that could carry out the insertion of an IOL satisfactorily, embodying the above-cited principle.
The insertion device, usually formed from plastic and often from polypropylene, comprises a channel that at the proximal end is open, and communicates with a tubular channel that extends to a distal open end. In the operation of some insertion devices, the flexible IOL is placed in the open end of the channel in a folded configuration. In other insertion devices, the IOL becomes folded as a result of design features in the channel that promote folding. The distal end of the device is positioned at the incision in the eye and the IOL pushed through the channel and into the eye. In the presentation that follows, the untreated plastic device will be referred to as the “cartridge”.
The requirement that the IOL be moved through the device without damage is critically important, and a corollary requirement is that the passageway be adequately lubricated to reduce friction to a harmless level. The friction to be overcome is jointly characteristic of the IOL and haptic surfaces on the one hand, and the surface of the inner wall of the channel through which the lens is moved on the other hand; i.e., friction cannot be defined as a property of a single surface, but of both surfaces, either or both of which may be moving to generate the friction.
The problem of lubricating the insertion channel has been addressed, to some extent, in the prior art, including some of the patents cited above. For example, U.S. Pat. No. 4,681,102 briefly describes treating the lumen through which the IOL passes with a product known by the trademark Healon. Healon is a solution of sodium hyaluronate in water. A problem with the latter approach is that the Healon can be harmful if introduced into the eye, and not completely removed after the IOL is inserted.
U.S. Pat. No. 5,716,364 also is concerned with lubricating the interface between IOL and the cartridge wall, so as to reduce friction in the movement of the folded IOL. The patent describes the use of lubricants that are not covalently bonded to the surface of the inserter, such as glyceryl monostearate or polyvinylpyrrolidone (PVP). The lubricant is said to be incorporated uniformly throughout the polypropylene, presumably by mixing and compounding in an extruder or milling on plastics processing rolls, and because the lubricant and polypropylene are mutually incompatible, the lubricant blooms to the surface of the cartridge, where it acts to facilitate the passage of the IOL. For the very reason that the lubricant is not bonded chemically to the polypropylene and is therefore mobile and capable of moving to the surface of the cartridge wall, it can be carried along with the IOL and some of it also inserted into the eye. Either glyceryl monostearate or PVP is foreign contamination of the viscous fluid that fills the eye, and whether it will cause long-term problems can only be determined by years of clinical experience.
The same U.S. Pat. No. 5,716,364 also describes a covalently bonded lubricity enhancing component, but no teaching is made in this patent as to how glyceryl monostearate or PVP might be covalently bound to polypropylene.
In U.S. Pat. No. 5,803,925, the subject is an IOL inserter with a covalently bound lubricant of the type represented by the formula A-PEG, where A is a reactive group capable of bonding chemically to the surface of the cartridge, and PEG is polyethylene glycol or other hydrophilic (or oleophilic) polymer. In the operation of the inserter, the clean cartridge is soaked for about three hours in a solution of the A-PEG and is then subjected to UV irradiation to cause photolysis of the polypropylene and bonding of the A-PEG.
The covalently bonded and immobile “lubricant” does not lubricate adequately to facilitate the passage of the IOL through the pathway of the device. The patent states that a balanced salt solution of sodium hyaluronate (BSS) must be used along with the treated inserter in order to achieve sufficiently low friction for the IOL to pass, with the normal application of force. The patent reports the finding that neither the cartridge with bonded A-PEG but without BSS, nor the untreated cartridge with BSS alone, is effective in passing the folded IOL
The present invention comprises an IOL insertion device having a continuous, bilaminar, lubricious coating which is permanently bound to at least a portion of the inner surface of the channel through which an IOL passes. The coatings used with the insertion device of the present invention have been found to produce results that are superior to those of any of the known IOL insertion devices of the prior art.